Method for the removal of sulfur from sponge iron



Patented July 15, 1952 METHOD Secretary of the Interior I. N0 Drawing. Application Januar Serial No. {120,326

, UNITED? STAT- Es :B I I QFHCE j I U V 412,603,4725; 7' s I A i I FOR THE REMQVKI 'OF V V} ,Y FROM SPONGE H r v Russell, 0. Buehl, Edgewood. assignorto' the p ,7

United States ofAmericaas represented'bylthe I .s'cilims. ici. 241,-14) H a I (Granted underfthe act of 'March 3, 1883, as

amended April 30, 1928 3700. G. 75 7') The invention described herein maybe manu 'factured and used by or for the Government of ;the United States for governmental." purposes withoutthe payment to me of any royaltyjthereon in accordance with the provisions of'the act of April 30, 1928 (Ch. 460, 45"Stat. L. 467).

This'invention relates to the removal 'of-sulfur from metals reduced from their ores at temperatures sufiiciently low so that melting does not occur and, in particular, to the removal of sulfur fro-m sponge iron. 1

In order to produce certain grades of steel,

especially tool steels, it is necessary to use iron having a very low sulfur content, generally less than 0.06 percent sulfur by weight. Sponge iron has been found to be a desirable melting stock for the production of steels, especially tool steels in electric arc furnaces, but its sulfur content is often undesirably high for this application. Sponge iron can be produced economically and the sulfur content can be controlled by theme of lime, limestone, or dolomite as described in U. S. Patent 2,380,406 and in the Co-pending application of Buehl et al. Serial No. 778,452,

filed October 7, 1947, now United States Patent No. 2,495,225. However, these sulfur control agents increase the cost of production of the material and do not always yield sponge iron with as low a sulfur content as is desired. The

process herein described may be employed to advantage to further lower the sulfur content of abrading the surface of sulfur bearing sponge iron and separating therefrom the fines thereby broken from said surface, whereby a low sulfur bearing sponge iron product is produced.

The method accordingly comprises a means of surface layer is broken off as" powdered fines without appreciably decreasing the size'of the malleable sponge iron particles. Grinding equipment' that involves thefimpact, of the iron particles at high'velocities has been foundto accornplish the abradin'g in a satisfactory manner and is presently, preferred? Thereafter," the fines or the broken surface particles, are separated from the sponge? iron. particles by suitable particle classifying means such as sieving,'rnagnetic sep'a ration, sink and float separation,- air classification, and the like. The more massive particles so obtained are found to have a considerably lower sulfur content than the initial spongeiron product. i

The following examples show how the invention may be carried out, but it is not limited thereto. Percentages are by weight unless specifled to the contrary.

Example I A sample of sponge iron containing 0.061 percent sulfur was mechanically sieved to remove the minus 200 mesh particles; This sieving lowered the sulfur content of the sponge iron to 0.051 percent with a loss of only 1.9 percent of the iron content of the sample.

Example II A sponge iron containing 0.061 sulfur was ball milled for 10 minutes then sieved. The removal.

of the minus 325 mesh particles lowered the sulfur content of the sponge iron to 0.053 percent with a loss of 3.1 percent of the iron; and the removal of the minus 200 mesh particles lowered the sulfur content of the sponge iron to 0.045 percent with a loss of 8.2 percent of the iron.

Example III 7 'tent to 0.075 percent.

removing sulfur from sponge iron or other metals reduced from their ores at temperatures below the melting point of the constituents.

In operation, a sulfur bearing sponge iron product is subjected to suitable abrading treatment such as selective grinding, roll crushing,

While the invention has been particularly de- Q scribed employing specific abrading means, it is tumbling, and the like. By this action the brittle not limited thereto.

While the invention has been particularly described employing specific separating or classifying meansiitisi not limited thereto.- 7

Since -many apparently widely. differing -embodiments of the invention will occur to one skilled in the art, the invention is not limited to the specific details illustrated and described and various changes may be madetherern witheout departing from the spirit and scope thereof;

What is claimed is:

sponge iron which comprises treating the iron ore at a temperature below the melting point of the constituents of said ore in the presence; 7 15 of a solid carbonaceous material as the reducing agent and a desulfurizing agent selected from the group consisting of dolomite, lime and limestoneto produce sponge iron particles having a closely adhering, brittle surface coating of high sulfur content basic slag, then abrading the surface of the so produced sponge iron'particles'to re- "fnove .the brittle surface layenand then separating from the abraded sponge iron particles the fines of high sulfur content slag Which have been broken from the surface of said particles. "2;- The method of claim 1 wherein the abrad- 'ing is accomplished by b'allniill'g'rindi'ng.

is. The methodfof claim 1 wherein the abradin t H 10. 1. The method of producing low'sulfui' content lithe fines.

4 4. The method of claim 1 wherein the abrading is accomplished by roll crushing.

5. The method of claim: 1 wherein the abrading is accomplished by ball mill grinding and the separating is accomplished by sieving to remove RUSSELL C. BUEHL.

REFERENCES CITED The'fol-lovving references are of record inthe :file of this patent:

is accomplished by high velocity impact "grinding.

STATES PATENTS 

1. THE METHOD OF PRODUCING LOW SULFUR CONTENT SPONGE IRON WHICH COMPRISES TREATING THE IRON ORE AT A TEMPERATURE BELOW THE MELTING POINT OF THE CONSTITUENTS OF SAID ORE IN THE PRESENCE OF A SOLID CARBONACEOUS MATERIAL AS THE REDUCING AGENT AND A DESULFURIZING AGENT SELECTED FROM THE GROUP CONSISTING OF DOLOMITE, LIME AND LIMESTONE TO PRODUCE SPONGE IRON PARTICLES HAING A CLOSELY ADHERNG, BRITTLE SURFACE COATING OF HIGH SULFUR CONTENT BASIC SLAG, THEN ABRADING THE SURFACES OF THE SO PRODUCED SPONGE IRON PARTICLES TO REMOVE THE BRITTLE SURFACE LAYER, AND THEN SEPARATING FROM THE ABRADED SPONGE IRON PARTICLES THE FINES OF HIGH SLFUR CONTENT SLAG WHICH HAVE BEEN BROKEN FROM THE SURFACE OF SAID PARTICLES. 